calculus – Tangent Vector at a specific point

I was asked to parameterize the circle edge of d2 =${(x,y):x^2+y^2=9$ and $x+y>=0}$

enter image description here

Anyways I parametrized the circle edge within the bounds but now I have to find the tangent vector at (0, 3) and I am not exactly sure how to do that. Would I set (-3cos(t), 3sin(t)) equal to its bounds then solve first? Like -3cos(t)=pi/4, 3sin(t)=5pi/4 and then find r'(t)?

seo – robots meta tag for specific web crawler

<meta name="robots" content="index, follow">
<meta name="googlebot" content="index, follow, noimageindex">

Yes, this will “work” as intended, but can be simplified. Googlebot will merge the two and “will use the sum of the negative directives”, but there’s nothing to merge.

However, index and follow are the default actions and will simply be ignored. See the following related question: What is a difference in the order of “follow” and “index” in a robots meta tag?

So, the above could be simplified to a single element:

<meta name="googlebot" content="noimageindex">

If you don’t want images indexed by any bot (including Googlebot) that might support the noimageindex directive then you can “simplify” this further:

<meta name="robots" content="noimageindex">

Any bots (incl. Googlebot) that support noimageindex will honour it, those that don’t will ignore it. (This does assume that any other bots implementation is similar to that of Googlebot.)


filesystems – Disable atime update for specific files or folders

I hit an scenario where the update of the atime field in a Lustre file system from several simultaneous nodes performing reads on a single file is causing a severe performance loss.

Is there any way to ask an arbitrary command not to update the atime without having to mount the FS with the noatime option? Other users in the system could rely on this field for their operations, so I don’t want to do system wide changes, if possible.

I can add the O_NOATIME flag in my own compiled programs, but I need to use it in other tools like gzip.

8 – Override specific configuration keys in settings.local.php

I’m trying to learn the Drupal 8 configuration override system based on the documentation here:

As a simple test, I have disabled the Shield module and exported config. Here’s a diff:

diff --git a/config/sync/shield.settings.yml b/config/sync/shield.settings.yml
index 3f7482f18..d9f019ca4 100644
--- a/config/sync/shield.settings.yml
+++ b/config/sync/shield.settings.yml
@@ -1,4 +1,4 @@
-shield_enable: true
+shield_enable: false
 credential_provider: shield

Now, in my settings.local.php I have attempted to override this config key:

 * Disable Shield (HTTP Basic Authentication).
$config('shield')('shield_enable') = FALSE;

This approach does not seem to work.

Do I need to do anything else to override the configuration?

NOTE: This is a contrived example. I could use configuration splits to disable HTTP basic auth in the production environment, even if it’s enabled in the active database configuration. In fact, I am hoping this approach will allow me to use environment variables to provide environment-specific values for authentication tokens, API keys and other secrets that may change in sandbox and production environments, but details are irrelevant to the question.

seo – Replacing the public home page with member specific content for logged in users

Context: I am designing a web application that’s geared toward members-only features. There’s no site features that would be useful to non-members, so most of the website will only be available to authenticated users. Thus, the only public pages will be things like an About Us page (with contact options), a Features/Comparisons page (promote the service relative to competitors), and of course a Home Page.

Problem: My initial thought was that the homepage index.php file, located at the website root, should load the public content for non-authenticated visitors, but should load the main application landing page for authenticated users. My main reason was for members’ ease-of-access — automatic serving of the content they’re actually trying to get to if they’re already logged in, and no need to type / remember / bookmark a more complicated address than But this got me thinking whether that would work best in the long run for issues like SEO and maintainability.

Approaches: I can think of three:

  1. All files are hosted under, with no subdomains. When a visitor requests, it checks for authentication, and serves up the correct HTML depending. (This is the approach I mentioned above.)
  2. Public files are hosted under, while member-only pages are hosted under a subdomain like When an authenticated user attempts to access the public, they’ll be automatically redirected to
  3. The same as option 2, but instead of being automatically redirected, the user will stay on the public homepage, and will need to navigate to their application landing page via the main nav. (This approach seems best if some of the public pages actually have usefulness to authenticated users, which they won’t on my site, so I’m thinking this option doesn’t make sense?)

Which of these approaches would be best in terms of SEO, being easy to code, and easy to maintain?

How do I print a specific number of A based on a value from a cell in Google Sheets

There’s a cell that would contain the number of times a letter would be printed in a cell.


cell a1 = 3. b1 should look as “A A A”

my rough script is:

for(var arow=0; arow<4; arow++) {
  var numberofo = actsheet.getRange(arow+1,1).getValue();
     for(i=0; i<=numberofo;i++) {
         var test = actsheet.getRange(i+1,2).setValue("o");

Sorry the code looks rough. Haven’t coded for the last 7 years.

Magento 2 Exclude Free shipping method for specific products

I have created one attribute for products, if that attribute value is yes than only it will be eligible for free shipping and other products will be excluded from free shipping. so when i add that product in the cart it wont count in free shipping.

air travel – If I am going from Shenzhen to HK airport for an outbound flight, what are the covid specific rules and what airlines can I actually fly with

I am aware that sky pier and ferry service are open for SZ to HK at the moment, but not sure about the exact procedures and eligible airlines. The part of “upstream check in services” from the HK airport announcement confuses me a bit, since i have never used the pier before and I have no idea what is what there.

link to the announcement:

macbook pro – Allow a specific application “to administer your computer”

I get this dialog whenever python running under emacs calls at:

enter image description here

I want to grant Emacs a permanent permission to do that (preferably from the command line, without gui, so that I can automate it and don’t have to deal with the gui every time I recompile Emacs).

I tried adding Emacs (both GUI and the actual binary executable) to various places in the Security & Privacy (Privacy tab), e.g., Developer Tools, Full Disk Access, Files and Folders, but nothing changes.

There are related questions (How to turn off “terminal would like to administer your computer” message? and Reset All Mojave App Permissions) but, alas, they do not answer my question.